Like many, I suspect, in the moviegoing audience, I was unaware until I saw "Oranges and Sunshine" of a great government-sanctioned social scandal. Thousands of children in the mid-20th century were unjustly deported from Britain to Australia.

The children – almost all of whom were white, because the Australians were interested in "good white stock" – were separated from their parents, who were usually poor and deemed temporarily unfit to care for them. Kids as young as 4 were then told their parents had died. The parents, in turn, were informed, wrongly, that their children had been placed in foster homes and adopted by "better" families. In fact, they were shipped to Australia, where they were told they would be able to ride horses to school and romp in the land of "oranges and sunshine."

The reality was far different. Many were put to work as illegal laborers in church-sponsored institutions, the most notorious being the remote Roman Catholic orphanage in Bindoon, where physical and sexual abuse by the elders was reportedly rampant.

Aside from the Australian TV drama "The Leaving of Liverpool," there has never before been a mainstream movie about this outrage. "Oranges and Sunshine" is based on the 1996 nonfiction book "Empty Cradles," by Margaret Humphreys, a Nottingham-based English social worker who has done more than anybody else to uncover this story and reunite the "forgotten children" with their parents – those who are still alive. Emily Watson, an actress of surpassing skill, plays Margaret, and the film, set mostly in the 1980s, is told entirely from her point of view.

A lesser actress would have made an immediate play for our sympathies, but Watson, best known for her performance in "Breaking the Waves," brings out the steeliness in Margaret's social activism. Dressed primly even in the sultry Australian sunshine, Margaret is armored by decorum. Watson makes you feel the great emotional reserves beneath the armor.

The most powerful sequences in the movie are the linked vignettes involving Margaret and the various grown-up children whom she attempts to help in their search for – what, exactly? Closure? Catharsis? Margaret makes it clear that she can't give them back what they lost, and yet what she does retrieve for them is a piece of the identity that was shattered decades earlier.

Some of the adults, like the obstreperous Len (David Wenham), have learned to cope by walling off their grief. He tells Margaret he stopped crying at the age of 8 and doesn't know how to cry anymore. The most lost of the lost souls is probably Jack (a fine Hugo Weaving), who has recently been united with his sister from England and whose life has been a downward spiral of depression. Margaret's scene with him, where she sits him down and tells him the fate of his mother, is a marvel of impassioned restraint.

Director Jim Loach (the son of Ken Loach) and screenwriter Rona Munro don't milk the misery and they thankfully keep the film free of flashbacks to the children's ordeal. We can already see that ordeal etched deeply into their adult faces.

The downside to the filmmakers' approach is that, at times, "Oranges and Sunshine" has the tame tenor of a made-for-television movie. Margaret's valor, though we see the psychological strain it exacts on herself and her family, is presented a bit too tidily. She represents, at least in terms of the movie, a particular species of do-gooder: the champion of human rights who, through obsession and a will to change the world, neglects her own loved ones. I wish Loach had dug more deeply into that story. Heroism is no less heroic for being complicated.